Hey @plum​, our Canvas Kit is self-contained, so any of the request/response actions are tied to the Canvas Kit and the app. There's no way to use an external API to trigger an action in an app developed using our Canvas Kit. Can you tell me a little more about what you're looking to do here, please? Why do you need to call an external API?

I wanted to show the drop-down list in the app

can we create an app using reactjs code instead of using canvas kit,

What kind of drop-down list are you hoping to show? Can you give me more information about the app you're trying to build? The more you can share, the better I can help you.